The nail apparatus melanoma appears when a melanocyte present in a nail matrix cancerates. In a case of Japanese, it accounts for about 10% of malignant melanomas. Recuperation from the nail apparatus melanoma is considered to be unsatisfactory because making a definite diagnosis of the disease is difficult.
The melanocyte present in the nail matrix is inactive in a normal state and produces no melanin. In some cases, the melanocyte, whether or not it cancerates, starts to produce melanin. As the nail grows, the produced melanin forms a pattern called longitudinal melanonychia. If the melanocyte is not cancerous, the longitudinal melanonychia is considered to be a benign nevus. It is considered that the longitudinal melanonychia pattern allows to discriminate whether or not the melanocyte present in the nail matrix is cancerous. It is difficult, however, to make a definite diagnosis because visually inspecting the pattern with the use of a dermoscope and discriminating whether the pattern is a nevus or malignant one need rich experience and because, if it is a malignant melanoma, a biopsy is generally not beneficial to the patient. Such a difficulty is a factor of hindering recuperation. Accordingly, realizing a noninvasive and objective discrimination method of nail apparatus melanoma from benign longitudinal melanonychia is strongly needed by clinical sites.
To diagnose a malignant melanoma except a nail apparatus melanoma, various discrimination methods have been proposed based on “randomness” of the shape of an edge of the malignant melanoma. As one of the known means to quantify the randomness of a shape, there is a technique of using a pseudo-fractal dimension. Applying a tumor test, which uses only the pseudo-fractal dimension as an index, as it is to discriminating nail apparatus melanoma is difficult to surely discriminate whether the longitudinal melanonychia is malignant or benign. Among related arts, there is, for example, Japanese Unexamined Patent Application Publication No. 2008-154761.